This invention relates to a tin-borophosphate glass and to a sealing material using the same.
As a sealing material for various kinds of materials such as glass, ceramic, and metal, development has been made of a material using a sealing glass.
In order to obtain a strong bonding, it is necessary in a sealing process to heat the sealing glass to a temperature sufficient to wet a sealing surface of a sealed object. However, in sealing electronic components or parts, a sealing temperature must be kept as low as possible. Therefore, in such application, use is mainly made of a sealing material utilizing a low-melting-point lead-borate glass. Specifically, use is widely made of the material having a sealing temperature of 430-500.degree. C. and a thermal expansion coefficient of 70-100.times.10.sup.-7 /.degree. C.
However, it is recently required that no lead is contained in the sealing glass in view of the environmental problem.
As a lead-free sealing glass, a tin-phosphate glass has been proposed. However, such a glass contains a large amount of P.sub.2 O.sub.5 as a main glass-forming oxide and therefore tends to exhibit following defects inherent to a phosphate glass: 1) the thermal expansion coefficient is increased, 2) the mechanical strength is decreased in comparison with existing sealing glasses, 3) the weather resistance is degraded, 4) a glass component left uncrystallized is released or eluted, and 5) heavy bubbling occurs during vitrification because phosphate is used as a raw material. As a result, practical use is not yet commenced.